The only difference between a.c and d.c generator is that d.c uses split ring which enables current to be maintained in only one direction while a.c generator uses slip-ring which enables the cureent to flow sinusoidally.

d.c has split ring

C is the correct option

Question 5

The instantaneous value of the induced e.m.f. as a function of time is ε = εo sinwt where εo is the peak value of the
e.m.f. The instantaneous value of the e.m.f, one quarter of the period, is{UTME 2007}

A. εo B. εo/2 C. εo/4 D. 0

Solution

w = 2πf

f = 1/T

w = 2π / T

one quarter of the period will be

w = 2π / (T/4) =4* (2π / T)

ε = εo/4

C is the correct option

Question 6

From the diagram, the inductive reactance and the resistance R are respectively{UTME 2007}
A. 10Ω and 50Ω B. 20Ω and 50Ω C. 25Ω and 50Ω D. 50Ω and 45Ω

Solution

Xl = 2πFL = 2*π*50/π * 0.1 =10Ω

V = IZ

75 = 1.5*Z

Z = 75 /1.5 = 50Ω

Z = √R^2 + Xl^2

50 = √R^2 + 10^2

50^2 = R^2 + 100

2500 = R^2 + 100

R^2 = 2400

R = √2400 = 49.98Ω approximately = 50Ω

A is the correct option

Question 7

A transformer is rated 240V. If the primary coil is 4000 turns and the secondary voltage 12V, determine the number of turns in the secondary coil.{UTME 2005}
A. 100 B. 150 C. 200 D. 250